19F- and Fluorescently Labeled Micelles as Nanoscopic Assemblies for Chemotherapeutic Delivery

Micelles from amphiphilic star-block copolymers, having a hydrophobic hyperbranched core and amphiphilic fluoropolymer arms, were constructed as drug delivery agent assemblies. A series of polymer structures was constructed from consecutive copolymerizations of 4-chloromethy I styrene with dodecyl acrylate and then 1,1,1-trifluoroethyl methacrylate with tert-butyl acrylate, followed by acidolysis to release the hydrophilic acrylic acid residues. These structures were labeled with cascade blue as a fluorescence reporter. The series of materials differed primarily in the ratio of 1,1,1-trifluoroethyl methacrylate to acrylic acid units, to give differences in fluorine loading and hydrophobicity/hydrophilicity balance. Doxorubicin (DOX) was used as a therapeutic to study the loading, release, and cytotoxicity of these micellar constructs on an U87-MG-EGFRvIII-CBR cell line. The micelles, with TEM-measured diameters ranging 5-9 nm and DLS-measured hydrodynamic diameters 20-30 nm, had loading capacities of ca. 4 wt % of DOX. The DOX-loaded micelles exhibited potent cytotoxicity with cell viabilities of 60-25% at 1.0 mu g/mL effective DOX concentrations, depending upon the polymer composition, as determined by MTT assays. These cell viability values are comparable to that of free DOX, suggesting an effective release of the cargo and delivery to the cell nuclei, which was further confirmed by fluorescence microscopy of the cells. F-19-NMR spectroscopy indicated a partial degradation of the surface-available trifluoroethyl ester linkages of the micelles, which may have accelerated the release of DOX. 19F-NMR spectroscopy was also employed to confirm and to quantify the cell uptake of the micelles. These dual fluorescent- and F-19-labeled and chemically functional micelles may be used potentially in a variety of applications, such as cell labeling, imaging, and therapeutic delivery.